Types of ophthalmologic apparatuses include ophthalmologic imaging apparatuses for obtaining images of a subject's eye and ophthalmologic measuring apparatuses for measuring characteristics of a subject's eye.
Examples of the ophthalmologic imaging apparatus include an optical coherence tomography (OCT) apparatus for capturing a tomographic image by using OCT, a fundus camera for photographing the fundus, a scanning laser ophthalmoscope (SLO) for capturing an image of the fundus by laser scanning with the use of a confocal optical system, and the like.
Examples of the ophthalmologic measuring apparatuses include an eye refraction test apparatus (refractometer, keratometer) for measuring the refractive properties of the subject's eye, a tonometer, a specular microscope for obtaining the properties of the cornea (corneal thickness, cell distribution, etc.), a wavefront analyzer for obtaining the aberration information of the subject's eye by using a Hartmann-Shack sensor, and the like.
Regarding ophthalmologic examinations, in terms of precision and accuracy of examinations, position adjustment between the optical system of the apparatus and a subject's eve is very important. This position adjustment is referred to as alignment. Alignment includes the action of aligning the optical axis of the optical system of the apparatus with respect to the axis of a subject's eye (XY alignment), as well as the action of adjusting the distance between the subject's eye and the optical system of the apparatus (Z alignment).
There are various methods for alignment. As an exemplary method, a method, in which a light beam is projected on the cornea and alignment is performed by detecting its reflection image (Purkinje image), is know (see Japanese Unexamined Patent Application Publication No. 08-275921, for example).
Further, as a method realized in recent years, a method, in which a three-dimensional position of a subject's eye from two or more photographic images obtained by photographing an anterior segment from different directions and both XY alignment and Z alignment are performed based on the three-dimensional position, is known (see Japanese Unexamined Patent Application Publication No. 2013-248376, for example).